Replace FutureApiLevel with an ApiLevel.

Keeping the int constant around for now as FutureApiLevelInt because
it's still useful in places that haven't adopted ApiLevel yet for
testing if their non-ApiLevel API level is current or not.

Test: treehugger
Bug: http://b/154667674
Change-Id: I47a7012703f41fdeb56f91edf9c83afa93042deb

cc/compiler.go

@@ -392,7 +392,7 @@ func (compiler *baseCompiler) compilerFlags(ctx ModuleContext, flags Flags, deps
 	if ctx.Os().Class == android.Device {
 		version := ctx.sdkVersion()
 		if version == "" || version == "current" {
-			target += strconv.Itoa(android.FutureApiLevel)
+			target += strconv.Itoa(android.FutureApiLevelInt)
 		} else {
 			target += version
 		}